Process control systems, like those used in chemical, petroleum or other processes, typically include one or more process controllers communicatively coupled to at least one host or operator workstation and to one or more field devices via analog, digital or combined analog/digital buses or lines. The field devices, which may be, for example valves, valve positioners, switches and transmitters (e.g., temperature, pressure and flow rate sensors), perform functions within the process plant such as opening or closing valves and measuring process parameters. The process controllers receive signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices, use this information to implement control routines and then generate control signals which are sent over the buses or lines to the field devices to control the operation of the process. Information from the field devices and the controllers is typically made available to one or more applications executed by the operator workstation to enable an operator to perform any desired function with respect to the process, such as configuring the process, viewing the current state of the process, modifying the operation of the process, etc.
Additionally, in many processes, a separate safety system is provided to detect significant safety related problems within the process plant and to automatically close valves, remove power from devices, switch flows within the plant, etc., when a problem occurs which might result in or lead to a serious hazard in the plant, such as a spill of toxic chemicals, an explosion, etc. These safety systems typically have one or more separate controllers apart from the standard process control controllers, called logic solvers, which are connected to safety field devices via separate buses or communication lines installed within the process plant. The logic solvers use the safety field devices to detect process conditions associated with significant events, such as the position of certain safety switches or shutdown valves, overflows or underflows in the process, the operation of important power generation or control devices, the operation of fault detection devices, etc. to thereby detect “events” within the process plant. When an event (typically called a “cause”) is detected, the safety controller takes some action (typically called an “effect”) to limit the detrimental nature of the event, such as closing valves, turning devices off, removing power from sections of the plant, etc. Generally, these actions or effects include switching safety devices into a tripped or “safe” mode of operation which is designed to prevent a serious or hazardous condition within the process plant.
Systems within a process plant, such as process control systems and safety systems, typically may keep track statuses of various processes and/or the systems themselves. Input signals to a system may cause the status tracked by the system to change, and output signals generated by the system may depend on the current status of the system in addition to input signals to the system. Currently, the status of a system may be tracked using routines written in a programming language. Writing such routines can be tedious, time consuming and fraught with errors. In safety systems, such errors can be serious because a failure of the safety system to operate properly can lead to serious injury or even death on the part of plant personnel and to the destruction of potentially millions of dollars of equipment and material within a plant.
Also, the status of a system can be tracked using a programming technique for programmable controllers standardized by the International Electrotechnical Commission (IEC), commonly referred to as a “sequential function chart” (set forth in the IEC 61131-3 standard). But as is known to those of ordinary skill in the art, using a sequential function chart to keep track of the status of a system can be difficult. Additionally, similar to the routines written in a programming language, creating a sequential function chart can be tedious, time consuming and fraught with errors.